Vacuum discharge device and method of using the same



Dec. 10, 192.9. A. MUTSCHELLER Y 1,733,950 VACUUM DISCHARGE DEVICE ANDMETHOD OF USING THE SAME Filed March so, 1926 2 sheets-sheet 1 INVENTORflit/2w Mafia/teller ATTORNEY Dec. 10, 1929. r R 1,738,960

VACUUM DISCHARGE DEVICE AND METHOD OF usme .THE SAME Filed Mar ch so,1926 2 Sheets-Sheet 2 ATTOR'NEY Patented Dec. 10, 1929 PATENT OFFICEUNITED STATES ARTHUR MUTSCHELLEB, OF NEW YORK, N. Y.

V.AG'U"L'II'IMT DISCHARGE DEVICE AND METHOD OF USING THE SAMEApplication filed March 30, 1926. Serial No. 98,457.

and this cannot be done with any of the devices hitherto known in thisart.

Furthermore, through my invention I am able to vary, theoreticallywithout limit, those characteristics and constants which have heretoforebeen universally regarded as invariable and fixed, and which wereclaimed 2 and used to define such conditions as degree of vacuum andabsence or presence of positive ionization, etc., as described anddefined in the prior art. These new results therefore make up convincingproof that the principle underlying my invention has not been previouslyknown to those skilled in the art, and that. many new effects areobtainable through the application of my invention in the vacuumdischarge technique.

In order to visualize my invention in a general way, let us assume thatWe have before us a heated cathode facing toward the anode. Then if theedge is blunt and approaches a plane perpendicular to an imaginary lineconnecting the anode with the cathode, the current emitted obeys, in thevoltage region below saturation, the Lilienfeld-Langmuir equation, andin the saturation region obeys the Richardson equation. If, however, byl i one of the methods indicated, an electrostatic field isconcentratedupon the edge facing toward the anode and this edge is made increasinglysharper or is brought nearer to the anode, or rendered sharper and alsobrought nearer the anode, then the current will increase above therespective values called for by the foregoing equations.

Again, let us assume that we place to the rear of the heated cathode ashield, electrically connected therewith, and so shaped as toconcentrate an electrostatic field upon the heated portion of thecathode, then the current passing between the cathode and the anode willstill further increase above the values corresponding to those expressedin the equations above discussed.

Furthermore, by insulating the shield from the heated cathode andimpressing an adequate difference of negative potential between theshield and the cathode, there is then an increase in the amount ofcurrent passing through the tube above the corresponding values in theaforesaid equation, provided the potential applied to the shield isnegative relatively to the cathode. If the potential applied to theshield is positive relatively to the cathode, the value of the currentthrough the tube is decreased. It follows, therefore, that a much largerdischarge current can be obtained in instances where the potential ofthe shield is negative instead of positive relatively to the cathodeThus in one case, when the anode of the tube is positive, the cathode isnegative and. the shield is negative with respect to the cathode, thenthe resistance through the tube is greatly de creased and a considerablylarger current than that corresponding to the aforementioned equationsof the prior art will pass through the tube. If, however, the polarityat the electrodes of the tube and the potential be tween the shield andthe cathode are reversed, then the resistance of the tube isconsiderably greater than otherwise with the ordinary kinds of flatcathodes and. therefore, under otherwise like conditions, with my devicethere is a greater and more pronounced valve action than with the valvetubes of the prior art.

These features are particularly prominent and useful when high voltagealternating currents are to be rectified. This is due to the fact thatif any impulse in the desired direction tends to pass, the valve tubeofi'ers less resistance, and if an impulse in the undesired directiontends to pass, the valve tube offers more resistance than the usual typeof valve tubes would offer. This constitutes a materially improved andhighly valuable increased valve effect.

p assing (iii This applies to both casesof the discharge tube operatingbelow saturation as a valve tube, or above saturation as an X-ray tube.In a X-ray tube the feature of my invention enables the obtainin of alarger self-rectifying action of the tu if it is energized withalternatin current. But with the aid of a properly functionin device andby regulatmg the voltage on e shield with respect to m the cathode, itis possible to select the passage of any desired portion of the currentimplse, and on the other hand, to prevent a certain undesirable portionof the current im ulse from passing through the X-ray tube. uch devicesfor regulating the volta e on the shield with respect to the cath e maybe synchronously rotating contacts through which the voltage on theshield is either made of broken, or may be any static modulatory deviceconsistin of condensers and inductances capable 0% producing the desiredvoltage variation between the shield and the cath- By referring toFigures 4 and 5, the mode of action of my device as compared with the.discharge tubes of the prior art can easily be traced and understood byone skilled in the art.

The principle of my invention thus explained, I will next describecertain forms of apparatus which illustrate and embody the points inwhich my device differs from the various vacuum discharge tubes of theprior art. These forms are, however, only typical examples, andvariations from these constructions can be made without departing fromthe spirit of my invention.

Reference is made to the accompanying drawings forming a part of thisspecification, l k

and in which like reference characters indi cate like parts throughoutthe several figures.

Figure 1 is a longitudinal section, showing a form of vacuum dischar 0device made in accordance with my invention, and in which the heatedcathode presents a knife-like edge toward the anode.

Figure 2 is alongitudinal section showing another form of vacuumdischarge device embodying my invention, and in which the heated cathodepresents toward the anode a number of sharp points.

Figure 3 is a .section on the line 3-3 of Figure 1, and indicates theform of the cathode, as seen in cross section.

' Figure 4 is a diagram indicating the manner in which I bias thepolarity of the elec trostatic shield relatively to the cathode, so thatwhenever the anode is for the moment positive, the electrostatic shieldis more negative than the cathode.

Figure 5 is a diagram of the apparatus appearing inFigure 4, andindicates that whenever the anode is for the moment negative, theelectrostatic shield is less negative than 65 the cathode.

I will first described the form of my device ap earing in Figure 1.

n exhausted tube 4, in this instance made of glass, has ageneralellipsoidal form, and is provided with a pair of end portions 4, 4",each of substantially cylindrical shape. These end portions are providedwith inwardly extendin supporting members 5, 6.

Fitted upon t e cylindrlcal portions are a pair of end caps 7 8, made ofinsulating material such as hard rubber or some composition used as asubstitute therefor.

Extending through the supporting member 5 and thus sealed into the tubeare three metallic rods 9, 10, 11. The two rods 9 and 10 serve asconductors, and the rod 11, used primarily as a mechanical support, hasalso a unction as a conductor. The rods 9, 10 and 11, preferably made ofstout wire, are provided with terminal connections 12, 13, 14, which maybe binding posts or otherwise, as re uired.

n electrostatic shield appears at 15, and has enerally the form of apot. It is carried by tlie rod 11, and is provided with a flaringportion 16, integral with it and having the form of a brim. Locatedwithin the electrostatic shield 15, but insulated from it, is thecathode 17., This cathode has the general form of a cimeter, and isadapted to be heated. For this purpose it is at its ends connected withthe rods 9 and 10 through which it is energized. It is provided with asharp edge 17, like the edge of a knife or razor, as indicated in Figure3.

The electrostatic shield and the cathode are each made of highlrefractory metal, such as molybdenum, nicliel, tungsten or the By makinga conductive connection from the rod 10 to the rod 11, as for instanceby extending a bit of wire from the terminal 13 to the terminal 14, theelectrostatic shield 15 and cathode 17 can be connected together andthus caused to o erate as a unit.

I find that w en the cathode 17 is heated, the sharp edge 17 is thehottest part thereof.

The anode is shown at 18, and has the general form of an open pot,provided with a brim 19, and facing toward the cathode. The anode ismade of refractory material, such as tun sten or molybdenum.

The ano e is mounted upon a supporting member 20, also made of refractormetal, and having in this instance two rodike portions 21 and 22,extending through and sealed into the in-turned portion 6 of the X-raytube. The rod-like portion 21 also extends throu h the end cap 8, andcarries a terminal 23, w ich may be a binding post.

Thus the parts are so arranged that the cathode 17 presents its sharp,knife-like ed e 17 toward the adjacent concave face of t 1e anode 18. Itfollows that with my device in action a considerable portion of thedischarge takes place directly between the anode as a whole and thesharp edge of the cathode. Previous to the exhaustion of the X-ray tubethe anode and cathode, together with their supports, are freed fromoccluded gases in the manner well known, and the exhaustion of the tubeis made as thorough as possible.

My purpose in giving to the tube 4 the shape shown and above describedis to avoid the repulsive effects of electrons and ions which remainstored in the concave surfaces of bulbs of approximately spherical form.In my apparatus, the electrons and, ions, if free of the discharge, tendto recede into the ends of the X-ray tube and thus to become lesseffective in opposing, limiting or otherwise interfering with theelectron discharge taking place through the tube. For this purpose theX-ray tube may have, as here indi-.

cated, such form that its greatest cross diameter is approximatelydouble the cross diameter of either end portion 4 or 4*.

If as above described the electrostatic shield 16 be placed in directmetallic communication with the heated cathode 17, as for instance byextending a bit of wire from the terminal 13 to the terminal 14, and analternating current potential be impressed upon the'anode and cathode,the electrostatic shield will of course develop such differences inpotential relatively to the anode as are developed between the anode andcathode. Tf, however, the electrostatic shield remain disconnected fromthe cathode, and has impressed upon it from an outside source anelectromotive force independent of the difference of potential betweenthe anode and cathode, the operator by controlling the electromotiveforce bet-ween the electrostatic shield and cathode can regulate withgreat nicety the discharge through the tube.

T have made the discovery that with the K-ray tube subjected toalternations in potential, if the electrostatic, shield 15 has at anyparticular instant a potential which is negative relatively to thecathode 17, the discharge taking place through the X-ray tube is themaximum discharge obtainable. When, however, the current reversal takesplace so that for the moment the heated cathode becomes positiverelatively to the anode, and yet the electrostatic shield, controllablefrom outside, is positive relatively to the cathode, the dischargethrough the tube is greatly lessened,the electrons being apparentlyunable to leave the cathode, or at least unable to leap to the anode.Thus the valve action of the tube is greatly pronounced.

In the form shown in Figure 2 the essential principles are the same, butthe construction is somewhat different.

The tube is shown at 24, and is provided with inturned end portions 25,26, carrying end caps 27, 28.

A number of small metallic rods are shown at 29, 30, 31, 32, 33 and 34,all extending through the inturned end portion 25. The rods 29, 30 and34 are larger than the others, and extend through the end cap 27.

Supported upon the rods 29, 30, 31, 32 and 33 is a fine wire 35, made ofrefractory metal such as tungsten, molybdenum or the like, and bent atintervals to form sharp points 36, 37, 38, 89. In the particularlyinstance here shown, the wire may be considered as starting from the rod29 and ending upon the rod 30. The wire is heated by currents orimpulses supplied to it through these two rods, and there are four sharppoints arranged in crown formation. However, this number is purelyarbitrary, as a single point or any larger number may be used. While ashere shown the wire presents sharp points, it may if desired be made topresent a continuous linear edge, as required.

An electrostatic shield 40, made of refractory metal, and provided witha reverting edge 41 formed into abrim, is supported upon the rod 34.

Terminals 42, 43 and 44, which may be binding posts, are provided forthe rods 29, 30 and 34, and their use may be understood by reference tothe foregoing remarks relative to the members 12, 13 and 14.

The anode appears at 45, and is substantially pot shaped. It is providedwith an edge portion 46, formed into a brim, and is mounted upon tworods 47, 48, which. extend through the inturned end portion 26 of thetube, the rod 48 being longer than the rod 47 and extending through theend cap 28. The rod 48 carries a terminal 49, which may be a bindingpost.

Except as otherwise described, the structure and action of the structureshown in Figure 2 are the same as in Figure 1.

In Figures 4 and 5 I show in diagrammatic form the X-ray tube abovedescribed with reference to Figure 1, with the addition of a transformerapparatus arranged for energizing the tube and for biasing the potentialof the electrostatic shield relatively to the potential of the cathodethereof.

A high tension transformer appears at 50, 1

and is provided with a primary winding 51 and with a secondary winding52. A wire 53 extends from one end of the secondary winding to the tubeterminal 23, and a wire 54 extends from the opposite end of thesecondary winding to the tube terminal 14.

A tap wire 55 is connected with the secondary winding 52 at a pointintermediate the ends thereof, so as to tap off a few convolutions 52thereof, this tap wire being also connected to a wire 56, the latterbeing connected to the tube terminal 13. The wire 56 is connected withthe secondary winding 57 of a small heating transformer 58. Another wire59 leads from the secondary wind ing 57 of this transformer to the tubeterm1nal12.

The heating transformer 58 is provided with a primary winding 60 wherebyit is energized, in the manner well l nown in this art, the heatingtransformer being energized in phase with the high tension transformer50.

The plus and minus shown in Figures 4 and 5 indicate differences inpotential atdifferent points alon the secondary winding of the highpotential transformer, and thus render apparent the relative effects ofthese diflerences of potential upon the electrodes and parts immediatelyassociated therewith.

For instance in Figure 4 the condition of the secondary winding is suchthat the anode 18 is for the moment positive, the heated cathode 17negative, and the electrostatic shield 18 still more negative; but inFigure 5 the anode is for the moment energized negatively, the heatedcathode 17 being positlve and electrostatic shield 15 still morepositive. Thus it will be noted that the extremes of potential arealways greater between the anode and the electrostatic shield thanbetween the anode and cathode.

The result of this arrangement is that with the apparatus in thecondition indicated in Figure 4 the electrostatic shield 15, because itspotential is negative relatively to the cathode 17, has not only arepellant effect upon-the electrons hurled from the cathode, and thusdrives them toward the anode, but appears also to increase their number;whereas with the apparatus in the condition indicated in Figure 5, or inother words with the polarity of the hlgh tension transformer re- I donot limit myself to the precise apparatus shown as variations may bemade therein without departing from my invention, the scope of which iscommensurate with my claims.

Having thus described my invention, what claim as new and desire tosecure by Letters Patent is as follows:

.1. The method herein described of assisting the thermionic emissionbetween an anode of relatively lar e size and a cathode of small sizehaving a s arp edge, which consists in subjecting the cathode to thedouble effect of a repellant negative electrostatic field from a regionbehind the cathode, and an attractive positive electrostatic field, fromsaid anode of relatively lar e size upon said sharp edge of saidcathode, or the purpose of producing an attenuated ne ativeelectrostatic field in front of said cathode.

2. The method herein described of assisting the thermionic emissionbetween an anode and a cathode, and effecting a substantiallycontrollable discharge between the anode and the cathode, said cathodebeing heated to a temperature below the normal thermionic. disc argetemperature, by subjecting said cathode to the repellant action of anintensified negative electrostatic field back of the electron-emittingpartof the cathode, in order to produce an attenuated negativeelectrostatic field in front of said cathode.

Signed at Long Island City, in the count of Queens and State of NewYork, this 26th day of March 1926.

ARTHUR MUTSCHELLER.

versed, the electrostatic shield attracts instead of repels theelectrons hurled from the cathode, and thus diverts them in considerable.numbers from reaching the anode.

It follows that when the X-ray tube is energized by a transformerapparatus arranged as indicated in Fi ures 4 and 5, or by any otherapparatus in w ich the X-ray tube is subjected to alternations of highpotential,

the valvular action of the tube is greatl accentuated. That is to say,there is a li eral passage of electrons from the cathode to theanodewhen the ener 'zing current impulse is in one direction, an apractically complete stoppage of electrons when the energizing I currentimpulse is in the opposite direction.

his improves the character of the X-rays generated, and prevents thedeterioration or destructionof the tube in consequence of currentimpulses sent through the tube in the wront direction.

I find that with an X-ray tube or other vacuum discharge device made inaccordance with my invention there is no limitation due to a conditionof saturation, and no limitation due to the presence or absence ofinterfering positive ionization as in the prior art.

